1. Field of the Invention
The present patent application for industrial invention relates to a hip prosthesis conceived in such a way to save as much as possible the bone stock of the femur proximal end and without giving the complications that are found in other prosthetic types, such as coating prostheses.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
As it is known, the anatomy of the proximal femur has a spheroid surface called “femoral head”, which articulates with a cavity of dimensions corresponding to the femoral head, situated in the pelvis, called cotyle or acetabulum. These two anatomic formations make up the coxofemoral joint.
When it cannot be treated with medications or physiotherapy, the deterioration of the joint because of fractures or degenerative processes (coxarthrosis) finds a solution in the implant of a prosthesis.
A typical hip prosthesis is made up of three components:                a femoral component composed of a stem that is pressed inside the femoral channel which is suitably modeled with progressive milling to generate a seat having the same shape as the stem; alternatively, a similarstem is cemented;        a prosthetic head that is fixed onto the stem with a locking system technically known as “Morse taper”;        an acetabular cup complete with insert that articulates with the corresponding prosthetic head.        
The stem of the hip prosthesis is generally made of metal (normally titanium alloy), has a length of approximately 12-15 cm and a shape similar to the anatomic cast of the femoral channel. After being pressed inside the femoral channel, the stem is firmly fitted, adhering on the internal walls of the bone corticals. In order to introduce a stem of this type it is necessary to resect the femoral neck at the base and mill the inside of the femoral channel removing a large quantity of bone by using progressive rasps specific for each type of prosthesis.
US2004/0039449 discloses a prosthesis that does not save the neck of the femur. In fact the neck is totally removed. A long channel is obtained in the femur, wherein a long prosthetic stem is inserted. Such a prosthesis is not suitable for being mounted in the femur neck because it is implanted in the femoral channel.
In order to solve these drawbacks, in recent years the so-called “neck saving” prostheses have been implanted, wherein the size and shape of the stem are conceived in such a way that resection is performed not at the base of the femoral neck, but at the base of the femoral head, implanting a stem that is able to anchor in the metaphisiary region without attacking the femoral channel.
WO91/07932 discloses a prosthesis that saves the neck of the femur. A spherical head is fixed to the stem, resting on the corticals of the femoral neck, with the risk of reabsorption. On the spherical head an acetabular segment with hemispherical shape can slide. However, this type of configuration is impaired by regulation problems. The femoral stem ends with a “Morse taper” whereon the prosthetic head made of metal or ceramic is inserted, being articulated with the acetabular component. The acetabular component is formed of a metal cup that is fixed to the pelvis, either by means of pressure or screwing, after suitably boring the natural cotyle. In the metal cup a ceramic or polyethylene insert is positioned, which articulates with the prosthetic head.
WO2011/006852, in the name of the applicant, discloses a hip prosthesis suitable for saving the femoral neck. However, the acetabular cup cannot be implanted on all patients, especially in patients with dysplastic or low-depth acetabula. In fact, the prosthetic head is shaped as a hemispherical cap with a perfectly smooth external surface. Said prosthetic head has a double sphericity, i.e. a central portion is provided on the external surface of the prosthetic head, in correspondence of the hemisphere pole, which protrudes outwards, having a surface with substantially ovoidal or ellipsoidal profile to reproduce as much as possible the anatomy of the femoral head in order to adjust in the acetabular seat.
WO2011/112353 discloses a hip prosthesis that is similar to the one described in WO2011/006852. Such a hip prosthesis comprises a prosthetic head or acetabular cup that is perfectly hemispherical and smooth and provided with holes for screws used for fixing to the acetabular seat. The acetabular cup comprises a very long shank that is fixed to a ball, in such manner to define a gap between ball and acetabular cup, wherein a femoral cup can slide. In such a case, the stress suffered by the acetabular cup is completely discharged on the shank that is fixed to the ball. For this reason the shank must be very long (a length higher than the radius of the ball) and the ball must be very small with a diameter lower than 40 mm, i.e. a diameter lower than the diameter of a natural head of a femur.
Hip prostheses are known having an acetabular component that comprises a non-cemented metal cup coated with a porous material that stimulates the re-growth of the bone and a stem that receives a femoral head for the hip joint. The surgical technique used to implant the acetabular component provides for the following steps:                boring the natural cotyle with sharp mills in order to obtain an acetabular seat,        using a test prosthesis to identify the correct size of the acetabular component,        implanting the final prosthesis either by means of pressure or screwing in the acetabular seat obtained in the pelvis.        
In the implanted metal cup a ceramic or polyethylene insert is positioned, which articulates with the prosthetic head implanted on the femoral stem. The drawbacks of such a traditional prosthesis are the early detachment of the prosthesis caused by wear or failure of the insert of the acetabular cup and a high percentage of dislocations caused by the incorrect position of the prosthesis. The dislocation of a hip prosthesis occurs when the prosthetic head comes out of the acetabular seat called“cotyle”. The causes of a dislocation of the total hip prosthesis are several:                the prosthesis is not positioned correctly and is often instable,        extreme bending and rotation movements must be avoided especially immediately after the operation,        the access ways are more or less dislocating.        
US2012/265319 discloses an acetabular prosthesis with a flattened pole and an external roughened surface.
WO01/70141 discloses an acetabular cup with a flattened pole and ribs extending on the external surface to stabilize the prosthesis.
The object of the present invention is to eliminate the drawbacks of the prior art by disclosing a hip prosthesis that is able to save the neck of the femur and is versatile and suitable for being applied to various types of acetabular seats.
Another object of the present invention is to provide such a hip prosthesis that is reliable, long-lasting and capable of not dislocating the femur when the prosthesis is positioned.